/**
 * @file
 * Dynamic Host Configuration Protocol client
 *
 * @defgroup dhcp4 DHCPv4
 * @ingroup ip4
 * DHCP (IPv4) related functions
 * This is a DHCP client for the lwIP TCP/IP stack. It aims to conform
 * with RFC 2131 and RFC 2132.
 *
 * @todo:
 * - Support for interfaces other than Ethernet (SLIP, PPP, ...)
 *
 * Options:
 * @ref DHCP_COARSE_TIMER_SECS (recommended 60 which is a minute)
 * @ref DHCP_FINE_TIMER_MSECS (recommended 500 which equals TCP coarse timer)
 *
 * dhcp_start() starts a DHCP client instance which
 * configures the interface by obtaining an IP address lease and maintaining it.
 *
 * Use dhcp_release() to end the lease and use dhcp_stop()
 * to remove the DHCP client.
 *
 * @see netifapi_dhcp4
 */

/*
 * Copyright (c) 2001-2004 Leon Woestenberg <leon.woestenberg@gmx.net>
 * Copyright (c) 2001-2004 Axon Digital Design B.V., The Netherlands.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 * The Swedish Institute of Computer Science and Adam Dunkels
 * are specifically granted permission to redistribute this
 * source code.
 *
 * Author: Leon Woestenberg <leon.woestenberg@gmx.net>
 *
 */

#include "lwip/opt.h"

#if LWIP_IPV4 && LWIP_DHCP /* don't build if not configured for use in lwipopts.h */

#include "lwip/stats.h"
#include "lwip/mem.h"
#include "lwip/udp.h"
#include "lwip/ip_addr.h"
#include "lwip/netif.h"
#include "lwip/def.h"
#include "lwip/dhcp.h"
#include "lwip/autoip.h"
#include "lwip/dns.h"
#include "lwip/etharp.h"
#include "lwip/prot/dhcp.h"

#include <string.h>

/** DHCP_CREATE_RAND_XID: if this is set to 1, the xid is created using
 * LWIP_RAND() (this overrides DHCP_GLOBAL_XID)
 */
#ifndef DHCP_CREATE_RAND_XID
	#define DHCP_CREATE_RAND_XID        1
#endif

/** Default for DHCP_GLOBAL_XID is 0xABCD0000
 * This can be changed by defining DHCP_GLOBAL_XID and DHCP_GLOBAL_XID_HEADER, e.g.
 *  \#define DHCP_GLOBAL_XID_HEADER "stdlib.h"
 *  \#define DHCP_GLOBAL_XID rand()
 */
#ifdef DHCP_GLOBAL_XID_HEADER
	#include DHCP_GLOBAL_XID_HEADER /* include optional starting XID generation prototypes */
#endif

/** DHCP_OPTION_MAX_MSG_SIZE is set to the MTU
 * MTU is checked to be big enough in dhcp_start */
#define DHCP_MAX_MSG_LEN(netif)        (netif->mtu)
#define DHCP_MAX_MSG_LEN_MIN_REQUIRED  576
/** Minimum length for reply before packet is parsed */
#define DHCP_MIN_REPLY_LEN             44

#define REBOOT_TRIES                2

#if LWIP_DNS && LWIP_DHCP_MAX_DNS_SERVERS
	#if DNS_MAX_SERVERS > LWIP_DHCP_MAX_DNS_SERVERS
		#define LWIP_DHCP_PROVIDE_DNS_SERVERS LWIP_DHCP_MAX_DNS_SERVERS
	#else
		#define LWIP_DHCP_PROVIDE_DNS_SERVERS DNS_MAX_SERVERS
	#endif
#else
	#define LWIP_DHCP_PROVIDE_DNS_SERVERS 0
#endif

/** Option handling: options are parsed in dhcp_parse_reply
 * and saved in an array where other functions can load them from.
 * This might be moved into the struct dhcp (not necessarily since
 * lwIP is single-threaded and the array is only used while in recv
 * callback). */
enum dhcp_option_idx {
	DHCP_OPTION_IDX_OVERLOAD = 0,
	DHCP_OPTION_IDX_MSG_TYPE,
	DHCP_OPTION_IDX_SERVER_ID,
	DHCP_OPTION_IDX_LEASE_TIME,
	DHCP_OPTION_IDX_T1,
	DHCP_OPTION_IDX_T2,
	DHCP_OPTION_IDX_SUBNET_MASK,
	DHCP_OPTION_IDX_ROUTER,
#if LWIP_DHCP_PROVIDE_DNS_SERVERS
	DHCP_OPTION_IDX_DNS_SERVER,
	DHCP_OPTION_IDX_DNS_SERVER_LAST = DHCP_OPTION_IDX_DNS_SERVER + LWIP_DHCP_PROVIDE_DNS_SERVERS - 1,
#endif /* LWIP_DHCP_PROVIDE_DNS_SERVERS */
#if LWIP_DHCP_GET_NTP_SRV
	DHCP_OPTION_IDX_NTP_SERVER,
	DHCP_OPTION_IDX_NTP_SERVER_LAST = DHCP_OPTION_IDX_NTP_SERVER + LWIP_DHCP_MAX_NTP_SERVERS - 1,
#endif /* LWIP_DHCP_GET_NTP_SRV */
	DHCP_OPTION_IDX_MAX
};

/** Holds the decoded option values, only valid while in dhcp_recv.
    @todo: move this into struct dhcp? */
u32_t dhcp_rx_options_val[DHCP_OPTION_IDX_MAX];
/** Holds a flag which option was received and is contained in dhcp_rx_options_val,
    only valid while in dhcp_recv.
    @todo: move this into struct dhcp? */
u8_t  dhcp_rx_options_given[DHCP_OPTION_IDX_MAX];

static u8_t dhcp_discover_request_options[] = {
	DHCP_OPTION_SUBNET_MASK,
	DHCP_OPTION_ROUTER,
	DHCP_OPTION_BROADCAST
#if LWIP_DHCP_PROVIDE_DNS_SERVERS
	, DHCP_OPTION_DNS_SERVER
#endif /* LWIP_DHCP_PROVIDE_DNS_SERVERS */
#if LWIP_DHCP_GET_NTP_SRV
	, DHCP_OPTION_NTP
#endif /* LWIP_DHCP_GET_NTP_SRV */
};

#ifdef DHCP_GLOBAL_XID
	static u32_t xid;
	static u8_t xid_initialised;
#endif /* DHCP_GLOBAL_XID */

#define dhcp_option_given(dhcp, idx)          (dhcp_rx_options_given[idx] != 0)
#define dhcp_got_option(dhcp, idx)            (dhcp_rx_options_given[idx] = 1)
#define dhcp_clear_option(dhcp, idx)          (dhcp_rx_options_given[idx] = 0)
#define dhcp_clear_all_options(dhcp)          (memset(dhcp_rx_options_given, 0, sizeof(dhcp_rx_options_given)))
#define dhcp_get_option_value(dhcp, idx)      (dhcp_rx_options_val[idx])
#define dhcp_set_option_value(dhcp, idx, val) (dhcp_rx_options_val[idx] = (val))

static struct udp_pcb* dhcp_pcb;
static u8_t dhcp_pcb_refcount;

/* DHCP client state machine functions */
static err_t dhcp_discover(struct netif* netif);
static err_t dhcp_select(struct netif* netif);
static void dhcp_bind(struct netif* netif);
#if DHCP_DOES_ARP_CHECK
	static err_t dhcp_decline(struct netif* netif);
#endif /* DHCP_DOES_ARP_CHECK */
static err_t dhcp_rebind(struct netif* netif);
static err_t dhcp_reboot(struct netif* netif);
static void dhcp_set_state(struct dhcp* dhcp, u8_t new_state);

/* receive, unfold, parse and free incoming messages */
static void dhcp_recv(void* arg, struct udp_pcb* pcb, struct pbuf* p, const ip_addr_t* addr, u16_t port);

/* set the DHCP timers */
static void dhcp_timeout(struct netif* netif);
static void dhcp_t1_timeout(struct netif* netif);
static void dhcp_t2_timeout(struct netif* netif);

/* build outgoing messages */
/* create a DHCP message, fill in common headers */
static err_t dhcp_create_msg(struct netif* netif, struct dhcp* dhcp, u8_t message_type);
/* free a DHCP request */
static void dhcp_delete_msg(struct dhcp* dhcp);
/* add a DHCP option (type, then length in bytes) */
static void dhcp_option(struct dhcp* dhcp, u8_t option_type, u8_t option_len);
/* add option values */
static void dhcp_option_byte(struct dhcp* dhcp, u8_t value);
static void dhcp_option_short(struct dhcp* dhcp, u16_t value);
static void dhcp_option_long(struct dhcp* dhcp, u32_t value);
#if LWIP_NETIF_HOSTNAME
	static void dhcp_option_hostname(struct dhcp* dhcp, struct netif* netif);
#endif /* LWIP_NETIF_HOSTNAME */
/* always add the DHCP options trailer to end and pad */
static void dhcp_option_trailer(struct dhcp* dhcp);

/** Ensure DHCP PCB is allocated and bound */
static err_t
dhcp_inc_pcb_refcount(void)
{
	if(dhcp_pcb_refcount == 0) {
		LWIP_ASSERT("dhcp_inc_pcb_refcount(): memory leak", dhcp_pcb == NULL);

		/* allocate UDP PCB */
		dhcp_pcb = udp_new();

		if(dhcp_pcb == NULL) {
			return ERR_MEM;
		}

		ip_set_option(dhcp_pcb, SOF_BROADCAST);

		/* set up local and remote port for the pcb -> listen on all interfaces on all src/dest IPs */
		udp_bind(dhcp_pcb, IP4_ADDR_ANY, DHCP_CLIENT_PORT);
		udp_connect(dhcp_pcb, IP4_ADDR_ANY, DHCP_SERVER_PORT);
		udp_recv(dhcp_pcb, dhcp_recv, NULL);
	}

	dhcp_pcb_refcount++;

	return ERR_OK;
}

/** Free DHCP PCB if the last netif stops using it */
static void
dhcp_dec_pcb_refcount(void)
{
	LWIP_ASSERT("dhcp_pcb_refcount(): refcount error", (dhcp_pcb_refcount > 0));
	dhcp_pcb_refcount--;

	if(dhcp_pcb_refcount == 0) {
		udp_remove(dhcp_pcb);
		dhcp_pcb = NULL;
	}
}

/**
 * Back-off the DHCP client (because of a received NAK response).
 *
 * Back-off the DHCP client because of a received NAK. Receiving a
 * NAK means the client asked for something non-sensible, for
 * example when it tries to renew a lease obtained on another network.
 *
 * We clear any existing set IP address and restart DHCP negotiation
 * afresh (as per RFC2131 3.2.3).
 *
 * @param netif the netif under DHCP control
 */
static void
dhcp_handle_nak(struct netif* netif)
{
	struct dhcp* dhcp = netif_dhcp_data(netif);

	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_handle_nak(netif=%p) %c%c%"U16_F"\n",
	            (void*)netif, netif->name[0], netif->name[1], (u16_t)netif->num));
	/* Change to a defined state - set this before assigning the address
	   to ensure the callback can use dhcp_supplied_address() */
	dhcp_set_state(dhcp, DHCP_STATE_BACKING_OFF);
	/* remove IP address from interface (must no longer be used, as per RFC2131) */
	netif_set_addr(netif, IP4_ADDR_ANY4, IP4_ADDR_ANY4, IP4_ADDR_ANY4);
	/* We can immediately restart discovery */
	dhcp_discover(netif);
}

#if DHCP_DOES_ARP_CHECK
/**
 * Checks if the offered IP address is already in use.
 *
 * It does so by sending an ARP request for the offered address and
 * entering CHECKING state. If no ARP reply is received within a small
 * interval, the address is assumed to be free for use by us.
 *
 * @param netif the netif under DHCP control
 */
static void
dhcp_check(struct netif* netif)
{
	struct dhcp* dhcp = netif_dhcp_data(netif);
	err_t result;
	u16_t msecs;
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_check(netif=%p) %c%c\n", (void*)netif, (s16_t)netif->name[0],
	            (s16_t)netif->name[1]));
	dhcp_set_state(dhcp, DHCP_STATE_CHECKING);
	/* create an ARP query for the offered IP address, expecting that no host
	   responds, as the IP address should not be in use. */
	result = etharp_query(netif, &dhcp->offered_ip_addr, NULL);

	if(result != ERR_OK) {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING, ("dhcp_check: could not perform ARP query\n"));
	}

	if(dhcp->tries < 255) {
		dhcp->tries++;
	}

	msecs = 500;
	dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_check(): set request timeout %"U16_F" msecs\n", msecs));
}
#endif /* DHCP_DOES_ARP_CHECK */

/**
 * Remember the configuration offered by a DHCP server.
 *
 * @param netif the netif under DHCP control
 */
static void
dhcp_handle_offer(struct netif* netif)
{
	struct dhcp* dhcp = netif_dhcp_data(netif);

	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_handle_offer(netif=%p) %c%c%"U16_F"\n",
	            (void*)netif, netif->name[0], netif->name[1], (u16_t)netif->num));

	/* obtain the server address */
	if(dhcp_option_given(dhcp, DHCP_OPTION_IDX_SERVER_ID)) {
		ip_addr_set_ip4_u32(&dhcp->server_ip_addr, lwip_htonl(dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_SERVER_ID)));
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_STATE, ("dhcp_handle_offer(): server 0x%08"X32_F"\n",
		            ip4_addr_get_u32(ip_2_ip4(&dhcp->server_ip_addr))));
		/* remember offered address */
		ip4_addr_copy(dhcp->offered_ip_addr, dhcp->msg_in->yiaddr);
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_STATE, ("dhcp_handle_offer(): offer for 0x%08"X32_F"\n",
		            ip4_addr_get_u32(&dhcp->offered_ip_addr)));

		dhcp_select(netif);
	} else {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
		            ("dhcp_handle_offer(netif=%p) did not get server ID!\n", (void*)netif));
	}
}

/**
 * Select a DHCP server offer out of all offers.
 *
 * Simply select the first offer received.
 *
 * @param netif the netif under DHCP control
 * @return lwIP specific error (see error.h)
 */
static err_t
dhcp_select(struct netif* netif)
{
	struct dhcp* dhcp = netif_dhcp_data(netif);
	err_t result;
	u16_t msecs;
	u8_t i;

	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_select(netif=%p) %c%c%"U16_F"\n", (void*)netif, netif->name[0], netif->name[1], (u16_t)netif->num));
	dhcp_set_state(dhcp, DHCP_STATE_REQUESTING);

	/* create and initialize the DHCP message header */
	result = dhcp_create_msg(netif, dhcp, DHCP_REQUEST);

	if(result == ERR_OK) {
		dhcp_option(dhcp, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
		dhcp_option_short(dhcp, DHCP_MAX_MSG_LEN(netif));

		/* MUST request the offered IP address */
		dhcp_option(dhcp, DHCP_OPTION_REQUESTED_IP, 4);
		dhcp_option_long(dhcp, lwip_ntohl(ip4_addr_get_u32(&dhcp->offered_ip_addr)));

		dhcp_option(dhcp, DHCP_OPTION_SERVER_ID, 4);
		dhcp_option_long(dhcp, lwip_ntohl(ip4_addr_get_u32(ip_2_ip4(&dhcp->server_ip_addr))));

		dhcp_option(dhcp, DHCP_OPTION_PARAMETER_REQUEST_LIST, LWIP_ARRAYSIZE(dhcp_discover_request_options));

		for(i = 0; i < LWIP_ARRAYSIZE(dhcp_discover_request_options); i++) {
			dhcp_option_byte(dhcp, dhcp_discover_request_options[i]);
		}

#if LWIP_NETIF_HOSTNAME
		dhcp_option_hostname(dhcp, netif);
#endif /* LWIP_NETIF_HOSTNAME */

		dhcp_option_trailer(dhcp);
		/* shrink the pbuf to the actual content length */
		pbuf_realloc(dhcp->p_out, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + dhcp->options_out_len);

		/* send broadcast to any DHCP server */
		udp_sendto_if_src(dhcp_pcb, dhcp->p_out, IP_ADDR_BROADCAST, DHCP_SERVER_PORT, netif, IP4_ADDR_ANY);
		dhcp_delete_msg(dhcp);
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_select: REQUESTING\n"));
	} else {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING, ("dhcp_select: could not allocate DHCP request\n"));
	}

	if(dhcp->tries < 255) {
		dhcp->tries++;
	}

	msecs = (dhcp->tries < 6 ? 1 << dhcp->tries : 60) * 1000;
	dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_STATE, ("dhcp_select(): set request timeout %"U16_F" msecs\n", msecs));
	return result;
}

/**
 * The DHCP timer that checks for lease renewal/rebind timeouts.
 * Must be called once a minute (see @ref DHCP_COARSE_TIMER_SECS).
 */
void
dhcp_coarse_tmr(void)
{
	struct netif* netif = netif_list;
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_coarse_tmr()\n"));

	/* iterate through all network interfaces */
	while(netif != NULL) {
		/* only act on DHCP configured interfaces */
		struct dhcp* dhcp = netif_dhcp_data(netif);

		if((dhcp != NULL) && (dhcp->state != DHCP_STATE_OFF)) {
			/* compare lease time to expire timeout */
			if(dhcp->t0_timeout && (++dhcp->lease_used == dhcp->t0_timeout)) {
				LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_coarse_tmr(): t0 timeout\n"));
				/* this clients' lease time has expired */
				dhcp_release(netif);
				dhcp_discover(netif);
				/* timer is active (non zero), and triggers (zeroes) now? */
			} else if(dhcp->t2_rebind_time && (dhcp->t2_rebind_time-- == 1)) {
				LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_coarse_tmr(): t2 timeout\n"));
				/* this clients' rebind timeout triggered */
				dhcp_t2_timeout(netif);
				/* timer is active (non zero), and triggers (zeroes) now */
			} else if(dhcp->t1_renew_time && (dhcp->t1_renew_time-- == 1)) {
				LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_coarse_tmr(): t1 timeout\n"));
				/* this clients' renewal timeout triggered */
				dhcp_t1_timeout(netif);
			}
		}

		/* proceed to next netif */
		netif = netif->next;
	}
}

/**
 * DHCP transaction timeout handling (this function must be called every 500ms,
 * see @ref DHCP_FINE_TIMER_MSECS).
 *
 * A DHCP server is expected to respond within a short period of time.
 * This timer checks whether an outstanding DHCP request is timed out.
 */
void
dhcp_fine_tmr(void)
{
	struct netif* netif = netif_list;

	/* loop through netif's */
	while(netif != NULL) {
		struct dhcp* dhcp = netif_dhcp_data(netif);

		/* only act on DHCP configured interfaces */
		if(dhcp != NULL) {
			/* timer is active (non zero), and is about to trigger now */
			if(dhcp->request_timeout > 1) {
				dhcp->request_timeout--;
			} else if(dhcp->request_timeout == 1) {
				dhcp->request_timeout--;
				/* { netif->dhcp->request_timeout == 0 } */
				LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_fine_tmr(): request timeout\n"));
				/* this client's request timeout triggered */
				dhcp_timeout(netif);
			}
		}

		/* proceed to next network interface */
		netif = netif->next;
	}
}

/**
 * A DHCP negotiation transaction, or ARP request, has timed out.
 *
 * The timer that was started with the DHCP or ARP request has
 * timed out, indicating no response was received in time.
 *
 * @param netif the netif under DHCP control
 */
static void
dhcp_timeout(struct netif* netif)
{
	struct dhcp* dhcp = netif_dhcp_data(netif);

	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_timeout()\n"));

	/* back-off period has passed, or server selection timed out */
	if((dhcp->state == DHCP_STATE_BACKING_OFF) || (dhcp->state == DHCP_STATE_SELECTING)) {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_timeout(): restarting discovery\n"));
		dhcp_discover(netif);
		/* receiving the requested lease timed out */
	} else if(dhcp->state == DHCP_STATE_REQUESTING) {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_timeout(): REQUESTING, DHCP request timed out\n"));

		if(dhcp->tries <= 5) {
			dhcp_select(netif);
		} else {
			LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_timeout(): REQUESTING, releasing, restarting\n"));
			dhcp_release(netif);
			dhcp_discover(netif);
		}

#if DHCP_DOES_ARP_CHECK
		/* received no ARP reply for the offered address (which is good) */
	} else if(dhcp->state == DHCP_STATE_CHECKING) {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_timeout(): CHECKING, ARP request timed out\n"));

		if(dhcp->tries <= 1) {
			dhcp_check(netif);
			/* no ARP replies on the offered address,
			   looks like the IP address is indeed free */
		} else {
			/* bind the interface to the offered address */
			dhcp_bind(netif);
		}

#endif /* DHCP_DOES_ARP_CHECK */
	} else if(dhcp->state == DHCP_STATE_REBOOTING) {
		if(dhcp->tries < REBOOT_TRIES) {
			dhcp_reboot(netif);
		} else {
			dhcp_discover(netif);
		}
	}
}

/**
 * The renewal period has timed out.
 *
 * @param netif the netif under DHCP control
 */
static void
dhcp_t1_timeout(struct netif* netif)
{
	struct dhcp* dhcp = netif_dhcp_data(netif);

	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_STATE, ("dhcp_t1_timeout()\n"));

	if((dhcp->state == DHCP_STATE_REQUESTING) || (dhcp->state == DHCP_STATE_BOUND) ||
	        (dhcp->state == DHCP_STATE_RENEWING)) {
		/* just retry to renew - note that the rebind timer (t2) will
		 * eventually time-out if renew tries fail. */
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
		            ("dhcp_t1_timeout(): must renew\n"));
		/* This slightly different to RFC2131: DHCPREQUEST will be sent from state
		   DHCP_STATE_RENEWING, not DHCP_STATE_BOUND */
		dhcp_renew(netif);

		/* Calculate next timeout */
		if(((dhcp->t2_timeout - dhcp->lease_used) / 2) >= ((60 + DHCP_COARSE_TIMER_SECS / 2) / DHCP_COARSE_TIMER_SECS)) {
			dhcp->t1_renew_time = ((dhcp->t2_timeout - dhcp->lease_used) / 2);
		}
	}
}

/**
 * The rebind period has timed out.
 *
 * @param netif the netif under DHCP control
 */
static void
dhcp_t2_timeout(struct netif* netif)
{
	struct dhcp* dhcp = netif_dhcp_data(netif);

	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_t2_timeout()\n"));

	if((dhcp->state == DHCP_STATE_REQUESTING) || (dhcp->state == DHCP_STATE_BOUND) ||
	        (dhcp->state == DHCP_STATE_RENEWING) || (dhcp->state == DHCP_STATE_REBINDING)) {
		/* just retry to rebind */
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE,
		            ("dhcp_t2_timeout(): must rebind\n"));
		/* This slightly different to RFC2131: DHCPREQUEST will be sent from state
		   DHCP_STATE_REBINDING, not DHCP_STATE_BOUND */
		dhcp_rebind(netif);

		/* Calculate next timeout */
		if(((dhcp->t0_timeout - dhcp->lease_used) / 2) >= ((60 + DHCP_COARSE_TIMER_SECS / 2) / DHCP_COARSE_TIMER_SECS)) {
			dhcp->t2_rebind_time = ((dhcp->t0_timeout - dhcp->lease_used) / 2);
		}
	}
}

/**
 * Handle a DHCP ACK packet
 *
 * @param netif the netif under DHCP control
 */
static void
dhcp_handle_ack(struct netif* netif)
{
	struct dhcp* dhcp = netif_dhcp_data(netif);

#if LWIP_DHCP_PROVIDE_DNS_SERVERS || LWIP_DHCP_GET_NTP_SRV
	u8_t n;
#endif /* LWIP_DHCP_PROVIDE_DNS_SERVERS || LWIP_DHCP_GET_NTP_SRV */
#if LWIP_DHCP_GET_NTP_SRV
	ip4_addr_t ntp_server_addrs[LWIP_DHCP_MAX_NTP_SERVERS];
#endif

	/* clear options we might not get from the ACK */
	ip4_addr_set_zero(&dhcp->offered_sn_mask);
	ip4_addr_set_zero(&dhcp->offered_gw_addr);
#if LWIP_DHCP_BOOTP_FILE
	ip4_addr_set_zero(&dhcp->offered_si_addr);
#endif /* LWIP_DHCP_BOOTP_FILE */

	/* lease time given? */
	if(dhcp_option_given(dhcp, DHCP_OPTION_IDX_LEASE_TIME)) {
		/* remember offered lease time */
		dhcp->offered_t0_lease = dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_LEASE_TIME);
	}

	/* renewal period given? */
	if(dhcp_option_given(dhcp, DHCP_OPTION_IDX_T1)) {
		/* remember given renewal period */
		dhcp->offered_t1_renew = dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_T1);
	} else {
		/* calculate safe periods for renewal */
		dhcp->offered_t1_renew = dhcp->offered_t0_lease / 2;
	}

	/* renewal period given? */
	if(dhcp_option_given(dhcp, DHCP_OPTION_IDX_T2)) {
		/* remember given rebind period */
		dhcp->offered_t2_rebind = dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_T2);
	} else {
		/* calculate safe periods for rebinding (offered_t0_lease * 0.875 -> 87.5%)*/
		dhcp->offered_t2_rebind = (dhcp->offered_t0_lease * 7U) / 8U;
	}

	/* (y)our internet address */
	ip4_addr_copy(dhcp->offered_ip_addr, dhcp->msg_in->yiaddr);

#if LWIP_DHCP_BOOTP_FILE
	/* copy boot server address,
	   boot file name copied in dhcp_parse_reply if not overloaded */
	ip4_addr_copy(dhcp->offered_si_addr, dhcp->msg_in->siaddr);
#endif /* LWIP_DHCP_BOOTP_FILE */

	/* subnet mask given? */
	if(dhcp_option_given(dhcp, DHCP_OPTION_IDX_SUBNET_MASK)) {
		/* remember given subnet mask */
		ip4_addr_set_u32(&dhcp->offered_sn_mask, lwip_htonl(dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_SUBNET_MASK)));
		dhcp->subnet_mask_given = 1;
	} else {
		dhcp->subnet_mask_given = 0;
	}

	/* gateway router */
	if(dhcp_option_given(dhcp, DHCP_OPTION_IDX_ROUTER)) {
		ip4_addr_set_u32(&dhcp->offered_gw_addr, lwip_htonl(dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_ROUTER)));
	}

#if LWIP_DHCP_GET_NTP_SRV

	/* NTP servers */
	for(n = 0; (n < LWIP_DHCP_MAX_NTP_SERVERS) && dhcp_option_given(dhcp, DHCP_OPTION_IDX_NTP_SERVER + n); n++) {
		ip4_addr_set_u32(&ntp_server_addrs[n], lwip_htonl(dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_NTP_SERVER + n)));
	}

	dhcp_set_ntp_servers(n, ntp_server_addrs);
#endif /* LWIP_DHCP_GET_NTP_SRV */

#if LWIP_DHCP_PROVIDE_DNS_SERVERS

	/* DNS servers */
	for(n = 0; (n < LWIP_DHCP_PROVIDE_DNS_SERVERS) && dhcp_option_given(dhcp, DHCP_OPTION_IDX_DNS_SERVER + n); n++) {
		ip_addr_t dns_addr;
		ip_addr_set_ip4_u32(&dns_addr, lwip_htonl(dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_DNS_SERVER + n)));
		dns_setserver(n, &dns_addr);
	}

#endif /* LWIP_DHCP_PROVIDE_DNS_SERVERS */
}

/**
 * @ingroup dhcp4
 * Set a statically allocated struct dhcp to work with.
 * Using this prevents dhcp_start to allocate it using mem_malloc.
 *
 * @param netif the netif for which to set the struct dhcp
 * @param dhcp (uninitialised) dhcp struct allocated by the application
 */
void
dhcp_set_struct(struct netif* netif, struct dhcp* dhcp)
{
	LWIP_ASSERT("netif != NULL", netif != NULL);
	LWIP_ASSERT("dhcp != NULL", dhcp != NULL);
	LWIP_ASSERT("netif already has a struct dhcp set", netif_dhcp_data(netif) == NULL);

	/* clear data structure */
	memset(dhcp, 0, sizeof(struct dhcp));
	/* dhcp_set_state(&dhcp, DHCP_STATE_OFF); */
	netif_set_client_data(netif, LWIP_NETIF_CLIENT_DATA_INDEX_DHCP, dhcp);
}

/**
 * @ingroup dhcp4
 * Removes a struct dhcp from a netif.
 *
 * ATTENTION: Only use this when not using dhcp_set_struct() to allocate the
 *            struct dhcp since the memory is passed back to the heap.
 *
 * @param netif the netif from which to remove the struct dhcp
 */
void dhcp_cleanup(struct netif* netif)
{
	LWIP_ASSERT("netif != NULL", netif != NULL);

	if(netif_dhcp_data(netif) != NULL) {
		mem_free(netif_dhcp_data(netif));
		netif_set_client_data(netif, LWIP_NETIF_CLIENT_DATA_INDEX_DHCP, NULL);
	}
}

/**
 * @ingroup dhcp4
 * Start DHCP negotiation for a network interface.
 *
 * If no DHCP client instance was attached to this interface,
 * a new client is created first. If a DHCP client instance
 * was already present, it restarts negotiation.
 *
 * @param netif The lwIP network interface
 * @return lwIP error code
 * - ERR_OK - No error
 * - ERR_MEM - Out of memory
 */
err_t
dhcp_start(struct netif* netif)
{
	struct dhcp* dhcp;
	err_t result;

	LWIP_ERROR("netif != NULL", (netif != NULL), return ERR_ARG;);
	LWIP_ERROR("netif is not up, old style port?", netif_is_up(netif), return ERR_ARG;);
	dhcp = netif_dhcp_data(netif);
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_start(netif=%p) %c%c%"U16_F"\n", (void*)netif, netif->name[0], netif->name[1], (u16_t)netif->num));

	/* check MTU of the netif */
	if(netif->mtu < DHCP_MAX_MSG_LEN_MIN_REQUIRED) {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): Cannot use this netif with DHCP: MTU is too small\n"));
		return ERR_MEM;
	}

	/* no DHCP client attached yet? */
	if(dhcp == NULL) {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): starting new DHCP client\n"));
		dhcp = (struct dhcp*)mem_malloc(sizeof(struct dhcp));

		if(dhcp == NULL) {
			LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): could not allocate dhcp\n"));
			return ERR_MEM;
		}

		/* store this dhcp client in the netif */
		netif_set_client_data(netif, LWIP_NETIF_CLIENT_DATA_INDEX_DHCP, dhcp);
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): allocated dhcp"));
		/* already has DHCP client attached */
	} else {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_start(): restarting DHCP configuration\n"));
		LWIP_ASSERT("pbuf p_out wasn't freed", dhcp->p_out == NULL);
		LWIP_ASSERT("reply wasn't freed", dhcp->msg_in == NULL);

		if(dhcp->pcb_allocated != 0) {
			dhcp_dec_pcb_refcount(); /* free DHCP PCB if not needed any more */
		}

		/* dhcp is cleared below, no need to reset flag*/
	}

	/* clear data structure */
	memset(dhcp, 0, sizeof(struct dhcp));
	/* dhcp_set_state(&dhcp, DHCP_STATE_OFF); */

	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_start(): starting DHCP configuration\n"));

	if(dhcp_inc_pcb_refcount() != ERR_OK) {  /* ensure DHCP PCB is allocated */
		return ERR_MEM;
	}

	dhcp->pcb_allocated = 1;

#if LWIP_DHCP_CHECK_LINK_UP

	if(!netif_is_link_up(netif)) {
		/* set state INIT and wait for dhcp_network_changed() to call dhcp_discover() */
		dhcp_set_state(dhcp, DHCP_STATE_INIT);
		return ERR_OK;
	}

#endif /* LWIP_DHCP_CHECK_LINK_UP */


	/* (re)start the DHCP negotiation */
	result = dhcp_discover(netif);

	if(result != ERR_OK) {
		/* free resources allocated above */
		dhcp_stop(netif);
		return ERR_MEM;
	}

	return result;
}

/**
 * @ingroup dhcp4
 * Inform a DHCP server of our manual configuration.
 *
 * This informs DHCP servers of our fixed IP address configuration
 * by sending an INFORM message. It does not involve DHCP address
 * configuration, it is just here to be nice to the network.
 *
 * @param netif The lwIP network interface
 */
void
dhcp_inform(struct netif* netif)
{
	struct dhcp dhcp;
	err_t result = ERR_OK;

	LWIP_ERROR("netif != NULL", (netif != NULL), return;);

	if(dhcp_inc_pcb_refcount() != ERR_OK) {  /* ensure DHCP PCB is allocated */
		return;
	}

	memset(&dhcp, 0, sizeof(struct dhcp));
	dhcp_set_state(&dhcp, DHCP_STATE_INFORMING);

	/* create and initialize the DHCP message header */
	result = dhcp_create_msg(netif, &dhcp, DHCP_INFORM);

	if(result == ERR_OK) {
		dhcp_option(&dhcp, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
		dhcp_option_short(&dhcp, DHCP_MAX_MSG_LEN(netif));

		dhcp_option_trailer(&dhcp);

		pbuf_realloc(dhcp.p_out, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + dhcp.options_out_len);

		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_inform: INFORMING\n"));

		udp_sendto_if(dhcp_pcb, dhcp.p_out, IP_ADDR_BROADCAST, DHCP_SERVER_PORT, netif);

		dhcp_delete_msg(&dhcp);
	} else {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("dhcp_inform: could not allocate DHCP request\n"));
	}

	dhcp_dec_pcb_refcount(); /* delete DHCP PCB if not needed any more */
}

/** Handle a possible change in the network configuration.
 *
 * This enters the REBOOTING state to verify that the currently bound
 * address is still valid.
 */
void
dhcp_network_changed(struct netif* netif)
{
	struct dhcp* dhcp = netif_dhcp_data(netif);

	if(!dhcp)
		return;

	switch(dhcp->state) {
		case DHCP_STATE_REBINDING:
		case DHCP_STATE_RENEWING:
		case DHCP_STATE_BOUND:
		case DHCP_STATE_REBOOTING:
			dhcp->tries = 0;
			dhcp_reboot(netif);
			break;

		case DHCP_STATE_OFF:
			/* stay off */
			break;

		default:
			/* INIT/REQUESTING/CHECKING/BACKING_OFF restart with new 'rid' because the
			   state changes, SELECTING: continue with current 'rid' as we stay in the
			   same state */
#if LWIP_DHCP_AUTOIP_COOP
			if(dhcp->autoip_coop_state == DHCP_AUTOIP_COOP_STATE_ON) {
				autoip_stop(netif);
				dhcp->autoip_coop_state = DHCP_AUTOIP_COOP_STATE_OFF;
			}

#endif /* LWIP_DHCP_AUTOIP_COOP */
			/* ensure we start with short timeouts, even if already discovering */
			dhcp->tries = 0;
			dhcp_discover(netif);
			break;
	}
}

#if DHCP_DOES_ARP_CHECK
/**
 * Match an ARP reply with the offered IP address:
 * check whether the offered IP address is not in use using ARP
 *
 * @param netif the network interface on which the reply was received
 * @param addr The IP address we received a reply from
 */
void
dhcp_arp_reply(struct netif* netif, const ip4_addr_t* addr)
{
	struct dhcp* dhcp;

	LWIP_ERROR("netif != NULL", (netif != NULL), return;);
	dhcp = netif_dhcp_data(netif);
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_arp_reply()\n"));

	/* is a DHCP client doing an ARP check? */
	if((dhcp != NULL) && (dhcp->state == DHCP_STATE_CHECKING)) {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_arp_reply(): CHECKING, arp reply for 0x%08"X32_F"\n",
		            ip4_addr_get_u32(addr)));

		/* did a host respond with the address we
		   were offered by the DHCP server? */
		if(ip4_addr_cmp(addr, &dhcp->offered_ip_addr)) {
			/* we will not accept the offered address */
			LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE | LWIP_DBG_LEVEL_WARNING,
			            ("dhcp_arp_reply(): arp reply matched with offered address, declining\n"));
			dhcp_decline(netif);
		}
	}
}

/**
 * Decline an offered lease.
 *
 * Tell the DHCP server we do not accept the offered address.
 * One reason to decline the lease is when we find out the address
 * is already in use by another host (through ARP).
 *
 * @param netif the netif under DHCP control
 */
static err_t
dhcp_decline(struct netif* netif)
{
	struct dhcp* dhcp = netif_dhcp_data(netif);
	err_t result = ERR_OK;
	u16_t msecs;
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_decline()\n"));
	dhcp_set_state(dhcp, DHCP_STATE_BACKING_OFF);
	/* create and initialize the DHCP message header */
	result = dhcp_create_msg(netif, dhcp, DHCP_DECLINE);

	if(result == ERR_OK) {
		dhcp_option(dhcp, DHCP_OPTION_REQUESTED_IP, 4);
		dhcp_option_long(dhcp, lwip_ntohl(ip4_addr_get_u32(&dhcp->offered_ip_addr)));

		dhcp_option_trailer(dhcp);
		/* resize pbuf to reflect true size of options */
		pbuf_realloc(dhcp->p_out, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + dhcp->options_out_len);

		/* per section 4.4.4, broadcast DECLINE messages */
		udp_sendto_if_src(dhcp_pcb, dhcp->p_out, IP_ADDR_BROADCAST, DHCP_SERVER_PORT, netif, IP4_ADDR_ANY);
		dhcp_delete_msg(dhcp);
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_decline: BACKING OFF\n"));
	} else {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
		            ("dhcp_decline: could not allocate DHCP request\n"));
	}

	if(dhcp->tries < 255) {
		dhcp->tries++;
	}

	msecs = 10 * 1000;
	dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_decline(): set request timeout %"U16_F" msecs\n", msecs));
	return result;
}
#endif /* DHCP_DOES_ARP_CHECK */


/**
 * Start the DHCP process, discover a DHCP server.
 *
 * @param netif the netif under DHCP control
 */
static err_t
dhcp_discover(struct netif* netif)
{
	struct dhcp* dhcp = netif_dhcp_data(netif);
	err_t result = ERR_OK;
	u16_t msecs;
	u8_t i;
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_discover()\n"));
	ip4_addr_set_any(&dhcp->offered_ip_addr);
	dhcp_set_state(dhcp, DHCP_STATE_SELECTING);
	/* create and initialize the DHCP message header */
	result = dhcp_create_msg(netif, dhcp, DHCP_DISCOVER);

	if(result == ERR_OK) {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_discover: making request\n"));

		dhcp_option(dhcp, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
		dhcp_option_short(dhcp, DHCP_MAX_MSG_LEN(netif));

		dhcp_option(dhcp, DHCP_OPTION_PARAMETER_REQUEST_LIST, LWIP_ARRAYSIZE(dhcp_discover_request_options));

		for(i = 0; i < LWIP_ARRAYSIZE(dhcp_discover_request_options); i++) {
			dhcp_option_byte(dhcp, dhcp_discover_request_options[i]);
		}

		dhcp_option_trailer(dhcp);

		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_discover: realloc()ing\n"));
		pbuf_realloc(dhcp->p_out, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + dhcp->options_out_len);

		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_discover: sendto(DISCOVER, IP_ADDR_BROADCAST, DHCP_SERVER_PORT)\n"));
		udp_sendto_if_src(dhcp_pcb, dhcp->p_out, IP_ADDR_BROADCAST, DHCP_SERVER_PORT, netif, IP4_ADDR_ANY);
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_discover: deleting()ing\n"));
		dhcp_delete_msg(dhcp);
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_discover: SELECTING\n"));
	} else {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("dhcp_discover: could not allocate DHCP request\n"));
	}

	if(dhcp->tries < 255) {
		dhcp->tries++;
	}

#if LWIP_DHCP_AUTOIP_COOP

	if(dhcp->tries >= LWIP_DHCP_AUTOIP_COOP_TRIES && dhcp->autoip_coop_state == DHCP_AUTOIP_COOP_STATE_OFF) {
		dhcp->autoip_coop_state = DHCP_AUTOIP_COOP_STATE_ON;
		autoip_start(netif);
	}

#endif /* LWIP_DHCP_AUTOIP_COOP */
	msecs = (dhcp->tries < 6 ? 1 << dhcp->tries : 60) * 1000;
	dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_discover(): set request timeout %"U16_F" msecs\n", msecs));
	return result;
}


/**
 * Bind the interface to the offered IP address.
 *
 * @param netif network interface to bind to the offered address
 */
static void
dhcp_bind(struct netif* netif)
{
	u32_t timeout;
	struct dhcp* dhcp;
	ip4_addr_t sn_mask, gw_addr;
	LWIP_ERROR("dhcp_bind: netif != NULL", (netif != NULL), return;);
	dhcp = netif_dhcp_data(netif);
	LWIP_ERROR("dhcp_bind: dhcp != NULL", (dhcp != NULL), return;);
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_bind(netif=%p) %c%c%"U16_F"\n", (void*)netif, netif->name[0], netif->name[1], (u16_t)netif->num));

	/* reset time used of lease */
	dhcp->lease_used = 0;

	if(dhcp->offered_t0_lease != 0xffffffffUL) {
		/* set renewal period timer */
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_bind(): t0 renewal timer %"U32_F" secs\n", dhcp->offered_t0_lease));
		timeout = (dhcp->offered_t0_lease + DHCP_COARSE_TIMER_SECS / 2) / DHCP_COARSE_TIMER_SECS;

		if(timeout > 0xffff) {
			timeout = 0xffff;
		}

		dhcp->t0_timeout = (u16_t)timeout;

		if(dhcp->t0_timeout == 0) {
			dhcp->t0_timeout = 1;
		}

		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_bind(): set request timeout %"U32_F" msecs\n", dhcp->offered_t0_lease * 1000));
	}

	/* temporary DHCP lease? */
	if(dhcp->offered_t1_renew != 0xffffffffUL) {
		/* set renewal period timer */
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_bind(): t1 renewal timer %"U32_F" secs\n", dhcp->offered_t1_renew));
		timeout = (dhcp->offered_t1_renew + DHCP_COARSE_TIMER_SECS / 2) / DHCP_COARSE_TIMER_SECS;

		if(timeout > 0xffff) {
			timeout = 0xffff;
		}

		dhcp->t1_timeout = (u16_t)timeout;

		if(dhcp->t1_timeout == 0) {
			dhcp->t1_timeout = 1;
		}

		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_bind(): set request timeout %"U32_F" msecs\n", dhcp->offered_t1_renew * 1000));
		dhcp->t1_renew_time = dhcp->t1_timeout;
	}

	/* set renewal period timer */
	if(dhcp->offered_t2_rebind != 0xffffffffUL) {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_bind(): t2 rebind timer %"U32_F" secs\n", dhcp->offered_t2_rebind));
		timeout = (dhcp->offered_t2_rebind + DHCP_COARSE_TIMER_SECS / 2) / DHCP_COARSE_TIMER_SECS;

		if(timeout > 0xffff) {
			timeout = 0xffff;
		}

		dhcp->t2_timeout = (u16_t)timeout;

		if(dhcp->t2_timeout == 0) {
			dhcp->t2_timeout = 1;
		}

		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_bind(): set request timeout %"U32_F" msecs\n", dhcp->offered_t2_rebind * 1000));
		dhcp->t2_rebind_time = dhcp->t2_timeout;
	}

	/* If we have sub 1 minute lease, t2 and t1 will kick in at the same time. */
	if((dhcp->t1_timeout >= dhcp->t2_timeout) && (dhcp->t2_timeout > 0)) {
		dhcp->t1_timeout = 0;
	}

	if(dhcp->subnet_mask_given) {
		/* copy offered network mask */
		ip4_addr_copy(sn_mask, dhcp->offered_sn_mask);
	} else {
		/* subnet mask not given, choose a safe subnet mask given the network class */
		u8_t first_octet = ip4_addr1(&dhcp->offered_ip_addr);

		if(first_octet <= 127) {
			ip4_addr_set_u32(&sn_mask, PP_HTONL(0xff000000UL));
		} else if(first_octet >= 192) {
			ip4_addr_set_u32(&sn_mask, PP_HTONL(0xffffff00UL));
		} else {
			ip4_addr_set_u32(&sn_mask, PP_HTONL(0xffff0000UL));
		}
	}

	ip4_addr_copy(gw_addr, dhcp->offered_gw_addr);

	/* gateway address not given? */
	if(ip4_addr_isany_val(gw_addr)) {
		/* copy network address */
		ip4_addr_get_network(&gw_addr, &dhcp->offered_ip_addr, &sn_mask);
		/* use first host address on network as gateway */
		ip4_addr_set_u32(&gw_addr, ip4_addr_get_u32(&gw_addr) | PP_HTONL(0x00000001UL));
	}

#if LWIP_DHCP_AUTOIP_COOP

	if(dhcp->autoip_coop_state == DHCP_AUTOIP_COOP_STATE_ON) {
		autoip_stop(netif);
		dhcp->autoip_coop_state = DHCP_AUTOIP_COOP_STATE_OFF;
	}

#endif /* LWIP_DHCP_AUTOIP_COOP */

	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_STATE, ("dhcp_bind(): IP: 0x%08"X32_F" SN: 0x%08"X32_F" GW: 0x%08"X32_F"\n",
	            ip4_addr_get_u32(&dhcp->offered_ip_addr), ip4_addr_get_u32(&sn_mask), ip4_addr_get_u32(&gw_addr)));
	/* netif is now bound to DHCP leased address - set this before assigning the address
	   to ensure the callback can use dhcp_supplied_address() */
	dhcp_set_state(dhcp, DHCP_STATE_BOUND);

	netif_set_addr(netif, &dhcp->offered_ip_addr, &sn_mask, &gw_addr);
	/* interface is used by routing now that an address is set */
}

/**
 * @ingroup dhcp4
 * Renew an existing DHCP lease at the involved DHCP server.
 *
 * @param netif network interface which must renew its lease
 */
err_t
dhcp_renew(struct netif* netif)
{
	struct dhcp* dhcp = netif_dhcp_data(netif);
	err_t result;
	u16_t msecs;
	u8_t i;
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_renew()\n"));
	dhcp_set_state(dhcp, DHCP_STATE_RENEWING);

	/* create and initialize the DHCP message header */
	result = dhcp_create_msg(netif, dhcp, DHCP_REQUEST);

	if(result == ERR_OK) {
		dhcp_option(dhcp, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
		dhcp_option_short(dhcp, DHCP_MAX_MSG_LEN(netif));

		dhcp_option(dhcp, DHCP_OPTION_PARAMETER_REQUEST_LIST, LWIP_ARRAYSIZE(dhcp_discover_request_options));

		for(i = 0; i < LWIP_ARRAYSIZE(dhcp_discover_request_options); i++) {
			dhcp_option_byte(dhcp, dhcp_discover_request_options[i]);
		}

#if LWIP_NETIF_HOSTNAME
		dhcp_option_hostname(dhcp, netif);
#endif /* LWIP_NETIF_HOSTNAME */

		/* append DHCP message trailer */
		dhcp_option_trailer(dhcp);

		pbuf_realloc(dhcp->p_out, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + dhcp->options_out_len);

		udp_sendto_if(dhcp_pcb, dhcp->p_out, &dhcp->server_ip_addr, DHCP_SERVER_PORT, netif);
		dhcp_delete_msg(dhcp);

		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_renew: RENEWING\n"));
	} else {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("dhcp_renew: could not allocate DHCP request\n"));
	}

	if(dhcp->tries < 255) {
		dhcp->tries++;
	}

	/* back-off on retries, but to a maximum of 20 seconds */
	msecs = dhcp->tries < 10 ? dhcp->tries * 2000 : 20 * 1000;
	dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_renew(): set request timeout %"U16_F" msecs\n", msecs));
	return result;
}

/**
 * Rebind with a DHCP server for an existing DHCP lease.
 *
 * @param netif network interface which must rebind with a DHCP server
 */
static err_t
dhcp_rebind(struct netif* netif)
{
	struct dhcp* dhcp = netif_dhcp_data(netif);
	err_t result;
	u16_t msecs;
	u8_t i;
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_rebind()\n"));
	dhcp_set_state(dhcp, DHCP_STATE_REBINDING);

	/* create and initialize the DHCP message header */
	result = dhcp_create_msg(netif, dhcp, DHCP_REQUEST);

	if(result == ERR_OK) {
		dhcp_option(dhcp, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
		dhcp_option_short(dhcp, DHCP_MAX_MSG_LEN(netif));

		dhcp_option(dhcp, DHCP_OPTION_PARAMETER_REQUEST_LIST, LWIP_ARRAYSIZE(dhcp_discover_request_options));

		for(i = 0; i < LWIP_ARRAYSIZE(dhcp_discover_request_options); i++) {
			dhcp_option_byte(dhcp, dhcp_discover_request_options[i]);
		}

#if LWIP_NETIF_HOSTNAME
		dhcp_option_hostname(dhcp, netif);
#endif /* LWIP_NETIF_HOSTNAME */

		dhcp_option_trailer(dhcp);

		pbuf_realloc(dhcp->p_out, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + dhcp->options_out_len);

		/* broadcast to server */
		udp_sendto_if(dhcp_pcb, dhcp->p_out, IP_ADDR_BROADCAST, DHCP_SERVER_PORT, netif);
		dhcp_delete_msg(dhcp);
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_rebind: REBINDING\n"));
	} else {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("dhcp_rebind: could not allocate DHCP request\n"));
	}

	if(dhcp->tries < 255) {
		dhcp->tries++;
	}

	msecs = dhcp->tries < 10 ? dhcp->tries * 1000 : 10 * 1000;
	dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_rebind(): set request timeout %"U16_F" msecs\n", msecs));
	return result;
}

/**
 * Enter REBOOTING state to verify an existing lease
 *
 * @param netif network interface which must reboot
 */
static err_t
dhcp_reboot(struct netif* netif)
{
	struct dhcp* dhcp = netif_dhcp_data(netif);
	err_t result;
	u16_t msecs;
	u8_t i;
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_reboot()\n"));
	dhcp_set_state(dhcp, DHCP_STATE_REBOOTING);

	/* create and initialize the DHCP message header */
	result = dhcp_create_msg(netif, dhcp, DHCP_REQUEST);

	if(result == ERR_OK) {
		dhcp_option(dhcp, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
		dhcp_option_short(dhcp, DHCP_MAX_MSG_LEN_MIN_REQUIRED);

		dhcp_option(dhcp, DHCP_OPTION_REQUESTED_IP, 4);
		dhcp_option_long(dhcp, lwip_ntohl(ip4_addr_get_u32(&dhcp->offered_ip_addr)));

		dhcp_option(dhcp, DHCP_OPTION_PARAMETER_REQUEST_LIST, LWIP_ARRAYSIZE(dhcp_discover_request_options));

		for(i = 0; i < LWIP_ARRAYSIZE(dhcp_discover_request_options); i++) {
			dhcp_option_byte(dhcp, dhcp_discover_request_options[i]);
		}

		dhcp_option_trailer(dhcp);

		pbuf_realloc(dhcp->p_out, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + dhcp->options_out_len);

		/* broadcast to server */
		udp_sendto_if(dhcp_pcb, dhcp->p_out, IP_ADDR_BROADCAST, DHCP_SERVER_PORT, netif);
		dhcp_delete_msg(dhcp);
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_reboot: REBOOTING\n"));
	} else {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("dhcp_reboot: could not allocate DHCP request\n"));
	}

	if(dhcp->tries < 255) {
		dhcp->tries++;
	}

	msecs = dhcp->tries < 10 ? dhcp->tries * 1000 : 10 * 1000;
	dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_reboot(): set request timeout %"U16_F" msecs\n", msecs));
	return result;
}


/**
 * @ingroup dhcp4
 * Release a DHCP lease (usually called before @ref dhcp_stop).
 *
 * @param netif network interface which must release its lease
 */
err_t
dhcp_release(struct netif* netif)
{
	struct dhcp* dhcp = netif_dhcp_data(netif);
	err_t result;
	ip_addr_t server_ip_addr;
	u8_t is_dhcp_supplied_address;

	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_release()\n"));

	if(dhcp == NULL) {
		return ERR_ARG;
	}

	ip_addr_copy(server_ip_addr, dhcp->server_ip_addr);

	is_dhcp_supplied_address = dhcp_supplied_address(netif);

	/* idle DHCP client */
	dhcp_set_state(dhcp, DHCP_STATE_OFF);
	/* clean old DHCP offer */
	ip_addr_set_zero_ip4(&dhcp->server_ip_addr);
	ip4_addr_set_zero(&dhcp->offered_ip_addr);
	ip4_addr_set_zero(&dhcp->offered_sn_mask);
	ip4_addr_set_zero(&dhcp->offered_gw_addr);
#if LWIP_DHCP_BOOTP_FILE
	ip4_addr_set_zero(&dhcp->offered_si_addr);
#endif /* LWIP_DHCP_BOOTP_FILE */
	dhcp->offered_t0_lease = dhcp->offered_t1_renew = dhcp->offered_t2_rebind = 0;
	dhcp->t1_renew_time = dhcp->t2_rebind_time = dhcp->lease_used = dhcp->t0_timeout = 0;

	if(!is_dhcp_supplied_address) {
		/* don't issue release message when address is not dhcp-assigned */
		return ERR_OK;
	}

	/* create and initialize the DHCP message header */
	result = dhcp_create_msg(netif, dhcp, DHCP_RELEASE);

	if(result == ERR_OK) {
		dhcp_option(dhcp, DHCP_OPTION_SERVER_ID, 4);
		dhcp_option_long(dhcp, lwip_ntohl(ip4_addr_get_u32(ip_2_ip4(&server_ip_addr))));

		dhcp_option_trailer(dhcp);

		pbuf_realloc(dhcp->p_out, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + dhcp->options_out_len);

		udp_sendto_if(dhcp_pcb, dhcp->p_out, &server_ip_addr, DHCP_SERVER_PORT, netif);
		dhcp_delete_msg(dhcp);
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("dhcp_release: RELEASED, DHCP_STATE_OFF\n"));
	} else {
		/* sending release failed, but that's not a problem since the correct behaviour of dhcp does not rely on release */
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("dhcp_release: could not allocate DHCP request\n"));
	}

	/* remove IP address from interface (prevents routing from selecting this interface) */
	netif_set_addr(netif, IP4_ADDR_ANY4, IP4_ADDR_ANY4, IP4_ADDR_ANY4);

	return result;
}

/**
 * @ingroup dhcp4
 * Remove the DHCP client from the interface.
 *
 * @param netif The network interface to stop DHCP on
 */
void
dhcp_stop(struct netif* netif)
{
	struct dhcp* dhcp;
	LWIP_ERROR("dhcp_stop: netif != NULL", (netif != NULL), return;);
	dhcp = netif_dhcp_data(netif);

	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_stop()\n"));

	/* netif is DHCP configured? */
	if(dhcp != NULL) {
#if LWIP_DHCP_AUTOIP_COOP

		if(dhcp->autoip_coop_state == DHCP_AUTOIP_COOP_STATE_ON) {
			autoip_stop(netif);
			dhcp->autoip_coop_state = DHCP_AUTOIP_COOP_STATE_OFF;
		}

#endif /* LWIP_DHCP_AUTOIP_COOP */

		LWIP_ASSERT("reply wasn't freed", dhcp->msg_in == NULL);
		dhcp_set_state(dhcp, DHCP_STATE_OFF);

		if(dhcp->pcb_allocated != 0) {
			dhcp_dec_pcb_refcount(); /* free DHCP PCB if not needed any more */
			dhcp->pcb_allocated = 0;
		}
	}
}

/*
 * Set the DHCP state of a DHCP client.
 *
 * If the state changed, reset the number of tries.
 */
static void
dhcp_set_state(struct dhcp* dhcp, u8_t new_state)
{
	if(new_state != dhcp->state) {
		dhcp->state = new_state;
		dhcp->tries = 0;
		dhcp->request_timeout = 0;
	}
}

/*
 * Concatenate an option type and length field to the outgoing
 * DHCP message.
 *
 */
static void
dhcp_option(struct dhcp* dhcp, u8_t option_type, u8_t option_len)
{
	LWIP_ASSERT("dhcp_option: dhcp->options_out_len + 2 + option_len <= DHCP_OPTIONS_LEN", dhcp->options_out_len + 2U + option_len <= DHCP_OPTIONS_LEN);
	dhcp->msg_out->options[dhcp->options_out_len++] = option_type;
	dhcp->msg_out->options[dhcp->options_out_len++] = option_len;
}
/*
 * Concatenate a single byte to the outgoing DHCP message.
 *
 */
static void
dhcp_option_byte(struct dhcp* dhcp, u8_t value)
{
	LWIP_ASSERT("dhcp_option_byte: dhcp->options_out_len < DHCP_OPTIONS_LEN", dhcp->options_out_len < DHCP_OPTIONS_LEN);
	dhcp->msg_out->options[dhcp->options_out_len++] = value;
}

static void
dhcp_option_short(struct dhcp* dhcp, u16_t value)
{
	LWIP_ASSERT("dhcp_option_short: dhcp->options_out_len + 2 <= DHCP_OPTIONS_LEN", dhcp->options_out_len + 2U <= DHCP_OPTIONS_LEN);
	dhcp->msg_out->options[dhcp->options_out_len++] = (u8_t)((value & 0xff00U) >> 8);
	dhcp->msg_out->options[dhcp->options_out_len++] = (u8_t)(value & 0x00ffU);
}

static void
dhcp_option_long(struct dhcp* dhcp, u32_t value)
{
	LWIP_ASSERT("dhcp_option_long: dhcp->options_out_len + 4 <= DHCP_OPTIONS_LEN", dhcp->options_out_len + 4U <= DHCP_OPTIONS_LEN);
	dhcp->msg_out->options[dhcp->options_out_len++] = (u8_t)((value & 0xff000000UL) >> 24);
	dhcp->msg_out->options[dhcp->options_out_len++] = (u8_t)((value & 0x00ff0000UL) >> 16);
	dhcp->msg_out->options[dhcp->options_out_len++] = (u8_t)((value & 0x0000ff00UL) >> 8);
	dhcp->msg_out->options[dhcp->options_out_len++] = (u8_t)((value & 0x000000ffUL));
}

#if LWIP_NETIF_HOSTNAME
static void
dhcp_option_hostname(struct dhcp* dhcp, struct netif* netif)
{
	if(netif->hostname != NULL) {
		size_t namelen = strlen(netif->hostname);

		if(namelen > 0) {
			size_t len;
			const char* p = netif->hostname;
			/* Shrink len to available bytes (need 2 bytes for OPTION_HOSTNAME
			   and 1 byte for trailer) */
			size_t available = DHCP_OPTIONS_LEN - dhcp->options_out_len - 3;
			LWIP_ASSERT("DHCP: hostname is too long!", namelen <= available);
			len = LWIP_MIN(namelen, available);
			LWIP_ASSERT("DHCP: hostname is too long!", len <= 0xFF);
			dhcp_option(dhcp, DHCP_OPTION_HOSTNAME, (u8_t)len);

			while(len--) {
				dhcp_option_byte(dhcp, *p++);
			}
		}
	}
}
#endif /* LWIP_NETIF_HOSTNAME */

/**
 * Extract the DHCP message and the DHCP options.
 *
 * Extract the DHCP message and the DHCP options, each into a contiguous
 * piece of memory. As a DHCP message is variable sized by its options,
 * and also allows overriding some fields for options, the easy approach
 * is to first unfold the options into a contiguous piece of memory, and
 * use that further on.
 *
 */
static err_t
dhcp_parse_reply(struct dhcp* dhcp, struct pbuf* p)
{
	u8_t* options;
	u16_t offset;
	u16_t offset_max;
	u16_t options_idx;
	u16_t options_idx_max;
	struct pbuf* q;
	int parse_file_as_options = 0;
	int parse_sname_as_options = 0;

	/* clear received options */
	dhcp_clear_all_options(dhcp);

	/* check that beginning of dhcp_msg (up to and including chaddr) is in first pbuf */
	if(p->len < DHCP_SNAME_OFS) {
		return ERR_BUF;
	}

	dhcp->msg_in = (struct dhcp_msg*)p->payload;
#if LWIP_DHCP_BOOTP_FILE
	/* clear boot file name */
	dhcp->boot_file_name[0] = 0;
#endif /* LWIP_DHCP_BOOTP_FILE */

	/* parse options */

	/* start with options field */
	options_idx = DHCP_OPTIONS_OFS;
	/* parse options to the end of the received packet */
	options_idx_max = p->tot_len;
again:
	q = p;

	while((q != NULL) && (options_idx >= q->len)) {
		options_idx -= q->len;
		options_idx_max -= q->len;
		q = q->next;
	}

	if(q == NULL) {
		return ERR_BUF;
	}

	offset = options_idx;
	offset_max = options_idx_max;
	options = (u8_t*)q->payload;

	/* at least 1 byte to read and no end marker, then at least 3 bytes to read? */
	while((q != NULL) && (options[offset] != DHCP_OPTION_END) && (offset < offset_max)) {
		u8_t op = options[offset];
		u8_t len;
		u8_t decode_len = 0;
		int decode_idx = -1;
		u16_t val_offset = offset + 2;

		/* len byte might be in the next pbuf */
		if((offset + 1) < q->len) {
			len = options[offset + 1];
		} else {
			len = (q->next != NULL ? ((u8_t*)q->next->payload)[0] : 0);
		}

		/* LWIP_DEBUGF(DHCP_DEBUG, ("msg_offset=%"U16_F", q->len=%"U16_F, msg_offset, q->len)); */
		decode_len = len;

		switch(op) {
			/* case(DHCP_OPTION_END): handled above */
			case(DHCP_OPTION_PAD):
				/* special option: no len encoded */
				decode_len = len = 0;
				/* will be increased below */
				offset--;
				break;

			case(DHCP_OPTION_SUBNET_MASK):
				LWIP_ERROR("len == 4", len == 4, return ERR_VAL;);
				decode_idx = DHCP_OPTION_IDX_SUBNET_MASK;
				break;

			case(DHCP_OPTION_ROUTER):
				decode_len = 4; /* only copy the first given router */
				LWIP_ERROR("len >= decode_len", len >= decode_len, return ERR_VAL;);
				decode_idx = DHCP_OPTION_IDX_ROUTER;
				break;
#if LWIP_DHCP_PROVIDE_DNS_SERVERS

			case(DHCP_OPTION_DNS_SERVER):
				/* special case: there might be more than one server */
				LWIP_ERROR("len %% 4 == 0", len % 4 == 0, return ERR_VAL;);
				/* limit number of DNS servers */
				decode_len = LWIP_MIN(len, 4 * DNS_MAX_SERVERS);
				LWIP_ERROR("len >= decode_len", len >= decode_len, return ERR_VAL;);
				decode_idx = DHCP_OPTION_IDX_DNS_SERVER;
				break;
#endif /* LWIP_DHCP_PROVIDE_DNS_SERVERS */

			case(DHCP_OPTION_LEASE_TIME):
				LWIP_ERROR("len == 4", len == 4, return ERR_VAL;);
				decode_idx = DHCP_OPTION_IDX_LEASE_TIME;
				break;
#if LWIP_DHCP_GET_NTP_SRV

			case(DHCP_OPTION_NTP):
				/* special case: there might be more than one server */
				LWIP_ERROR("len %% 4 == 0", len % 4 == 0, return ERR_VAL;);
				/* limit number of NTP servers */
				decode_len = LWIP_MIN(len, 4 * LWIP_DHCP_MAX_NTP_SERVERS);
				LWIP_ERROR("len >= decode_len", len >= decode_len, return ERR_VAL;);
				decode_idx = DHCP_OPTION_IDX_NTP_SERVER;
				break;
#endif /* LWIP_DHCP_GET_NTP_SRV*/

			case(DHCP_OPTION_OVERLOAD):
				LWIP_ERROR("len == 1", len == 1, return ERR_VAL;);
				/* decode overload only in options, not in file/sname: invalid packet */
				LWIP_ERROR("overload in file/sname", options_idx == DHCP_OPTIONS_OFS, return ERR_VAL;);
				decode_idx = DHCP_OPTION_IDX_OVERLOAD;
				break;

			case(DHCP_OPTION_MESSAGE_TYPE):
				LWIP_ERROR("len == 1", len == 1, return ERR_VAL;);
				decode_idx = DHCP_OPTION_IDX_MSG_TYPE;
				break;

			case(DHCP_OPTION_SERVER_ID):
				LWIP_ERROR("len == 4", len == 4, return ERR_VAL;);
				decode_idx = DHCP_OPTION_IDX_SERVER_ID;
				break;

			case(DHCP_OPTION_T1):
				LWIP_ERROR("len == 4", len == 4, return ERR_VAL;);
				decode_idx = DHCP_OPTION_IDX_T1;
				break;

			case(DHCP_OPTION_T2):
				LWIP_ERROR("len == 4", len == 4, return ERR_VAL;);
				decode_idx = DHCP_OPTION_IDX_T2;
				break;

			default:
				decode_len = 0;
				LWIP_DEBUGF(DHCP_DEBUG, ("skipping option %"U16_F" in options\n", (u16_t)op));
				break;
		}

		offset += len + 2;

		if(decode_len > 0) {
			u32_t value = 0;
			u16_t copy_len;
decode_next:
			LWIP_ASSERT("check decode_idx", decode_idx >= 0 && decode_idx < DHCP_OPTION_IDX_MAX);

			if(!dhcp_option_given(dhcp, decode_idx)) {
				copy_len = LWIP_MIN(decode_len, 4);

				if(pbuf_copy_partial(q, &value, copy_len, val_offset) != copy_len) {
					return ERR_BUF;
				}

				if(decode_len > 4) {
					/* decode more than one u32_t */
					LWIP_ERROR("decode_len %% 4 == 0", decode_len % 4 == 0, return ERR_VAL;);
					dhcp_got_option(dhcp, decode_idx);
					dhcp_set_option_value(dhcp, decode_idx, lwip_htonl(value));
					decode_len -= 4;
					val_offset += 4;
					decode_idx++;
					goto decode_next;
				} else if(decode_len == 4) {
					value = lwip_ntohl(value);
				} else {
					LWIP_ERROR("invalid decode_len", decode_len == 1, return ERR_VAL;);
					value = ((u8_t*)&value)[0];
				}

				dhcp_got_option(dhcp, decode_idx);
				dhcp_set_option_value(dhcp, decode_idx, value);
			}
		}

		if(offset >= q->len) {
			offset -= q->len;
			offset_max -= q->len;

			if((offset < offset_max) && offset_max) {
				q = q->next;
				LWIP_ASSERT("next pbuf was null", q);
				options = (u8_t*)q->payload;
			} else {
				/* We've run out of bytes, probably no end marker. Don't proceed. */
				break;
			}
		}
	}

	/* is this an overloaded message? */
	if(dhcp_option_given(dhcp, DHCP_OPTION_IDX_OVERLOAD)) {
		u32_t overload = dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_OVERLOAD);
		dhcp_clear_option(dhcp, DHCP_OPTION_IDX_OVERLOAD);

		if(overload == DHCP_OVERLOAD_FILE) {
			parse_file_as_options = 1;
			LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("overloaded file field\n"));
		} else if(overload == DHCP_OVERLOAD_SNAME) {
			parse_sname_as_options = 1;
			LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("overloaded sname field\n"));
		} else if(overload == DHCP_OVERLOAD_SNAME_FILE) {
			parse_sname_as_options = 1;
			parse_file_as_options = 1;
			LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("overloaded sname and file field\n"));
		} else {
			LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("invalid overload option: %d\n", (int)overload));
		}

#if LWIP_DHCP_BOOTP_FILE

		if(!parse_file_as_options) {
			/* only do this for ACK messages */
			if(dhcp_option_given(dhcp, DHCP_OPTION_IDX_MSG_TYPE) &&
			        (dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_MSG_TYPE) == DHCP_ACK))

				/* copy bootp file name, don't care for sname (server hostname) */
				if(pbuf_copy_partial(p, dhcp->boot_file_name, DHCP_FILE_LEN - 1, DHCP_FILE_OFS) != (DHCP_FILE_LEN - 1)) {
					return ERR_BUF;
				}

			/* make sure the string is really NULL-terminated */
			dhcp->boot_file_name[DHCP_FILE_LEN - 1] = 0;
		}

#endif /* LWIP_DHCP_BOOTP_FILE */
	}

	if(parse_file_as_options) {
		/* if both are overloaded, parse file first and then sname (RFC 2131 ch. 4.1) */
		parse_file_as_options = 0;
		options_idx = DHCP_FILE_OFS;
		options_idx_max = DHCP_FILE_OFS + DHCP_FILE_LEN;
		goto again;
	} else if(parse_sname_as_options) {
		parse_sname_as_options = 0;
		options_idx = DHCP_SNAME_OFS;
		options_idx_max = DHCP_SNAME_OFS + DHCP_SNAME_LEN;
		goto again;
	}

	return ERR_OK;
}

/**
 * If an incoming DHCP message is in response to us, then trigger the state machine
 */
static void
dhcp_recv(void* arg, struct udp_pcb* pcb, struct pbuf* p, const ip_addr_t* addr, u16_t port)
{
	struct netif* netif = ip_current_input_netif();
	struct dhcp* dhcp = netif_dhcp_data(netif);
	struct dhcp_msg* reply_msg = (struct dhcp_msg*)p->payload;
	u8_t msg_type;
	u8_t i;

	LWIP_UNUSED_ARG(arg);

	/* Caught DHCP message from netif that does not have DHCP enabled? -> not interested */
	if((dhcp == NULL) || (dhcp->pcb_allocated == 0)) {
		goto free_pbuf_and_return;
	}

	LWIP_ASSERT("invalid server address type", IP_IS_V4(addr));

	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("dhcp_recv(pbuf = %p) from DHCP server %"U16_F".%"U16_F".%"U16_F".%"U16_F" port %"U16_F"\n", (void*)p,
	            ip4_addr1_16(ip_2_ip4(addr)), ip4_addr2_16(ip_2_ip4(addr)), ip4_addr3_16(ip_2_ip4(addr)), ip4_addr4_16(ip_2_ip4(addr)), port));
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("pbuf->len = %"U16_F"\n", p->len));
	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("pbuf->tot_len = %"U16_F"\n", p->tot_len));
	/* prevent warnings about unused arguments */
	LWIP_UNUSED_ARG(pcb);
	LWIP_UNUSED_ARG(addr);
	LWIP_UNUSED_ARG(port);

	LWIP_ASSERT("reply wasn't freed", dhcp->msg_in == NULL);

	if(p->len < DHCP_MIN_REPLY_LEN) {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING, ("DHCP reply message or pbuf too short\n"));
		goto free_pbuf_and_return;
	}

	if(reply_msg->op != DHCP_BOOTREPLY) {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING, ("not a DHCP reply message, but type %"U16_F"\n", (u16_t)reply_msg->op));
		goto free_pbuf_and_return;
	}

	/* iterate through hardware address and match against DHCP message */
	for(i = 0; i < netif->hwaddr_len && i < NETIF_MAX_HWADDR_LEN && i < DHCP_CHADDR_LEN; i++) {
		if(netif->hwaddr[i] != reply_msg->chaddr[i]) {
			LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
			            ("netif->hwaddr[%"U16_F"]==%02"X16_F" != reply_msg->chaddr[%"U16_F"]==%02"X16_F"\n",
			             (u16_t)i, (u16_t)netif->hwaddr[i], (u16_t)i, (u16_t)reply_msg->chaddr[i]));
			goto free_pbuf_and_return;
		}
	}

	/* match transaction ID against what we expected */
	if(lwip_ntohl(reply_msg->xid) != dhcp->xid) {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING,
		            ("transaction id mismatch reply_msg->xid(%"X32_F")!=dhcp->xid(%"X32_F")\n", lwip_ntohl(reply_msg->xid), dhcp->xid));
		goto free_pbuf_and_return;
	}

	/* option fields could be unfold? */
	if(dhcp_parse_reply(dhcp, p) != ERR_OK) {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
		            ("problem unfolding DHCP message - too short on memory?\n"));
		goto free_pbuf_and_return;
	}

	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("searching DHCP_OPTION_MESSAGE_TYPE\n"));

	/* obtain pointer to DHCP message type */
	if(!dhcp_option_given(dhcp, DHCP_OPTION_IDX_MSG_TYPE)) {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_WARNING, ("DHCP_OPTION_MESSAGE_TYPE option not found\n"));
		goto free_pbuf_and_return;
	}

	/* read DHCP message type */
	msg_type = (u8_t)dhcp_get_option_value(dhcp, DHCP_OPTION_IDX_MSG_TYPE);

	/* message type is DHCP ACK? */
	if(msg_type == DHCP_ACK) {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("DHCP_ACK received\n"));

		/* in requesting state? */
		if(dhcp->state == DHCP_STATE_REQUESTING) {
			dhcp_handle_ack(netif);
#if DHCP_DOES_ARP_CHECK

			if((netif->flags & NETIF_FLAG_ETHARP) != 0) {
				/* check if the acknowledged lease address is already in use */
				dhcp_check(netif);
			} else {
				/* bind interface to the acknowledged lease address */
				dhcp_bind(netif);
			}

#else
			/* bind interface to the acknowledged lease address */
			dhcp_bind(netif);
#endif
		}
		/* already bound to the given lease address? */
		else if((dhcp->state == DHCP_STATE_REBOOTING) || (dhcp->state == DHCP_STATE_REBINDING) ||
		        (dhcp->state == DHCP_STATE_RENEWING)) {
			dhcp_handle_ack(netif);
			dhcp_bind(netif);
		}
	}
	/* received a DHCP_NAK in appropriate state? */
	else if((msg_type == DHCP_NAK) &&
	        ((dhcp->state == DHCP_STATE_REBOOTING) || (dhcp->state == DHCP_STATE_REQUESTING) ||
	         (dhcp->state == DHCP_STATE_REBINDING) || (dhcp->state == DHCP_STATE_RENEWING))) {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("DHCP_NAK received\n"));
		dhcp_handle_nak(netif);
	}
	/* received a DHCP_OFFER in DHCP_STATE_SELECTING state? */
	else if((msg_type == DHCP_OFFER) && (dhcp->state == DHCP_STATE_SELECTING)) {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE, ("DHCP_OFFER received in DHCP_STATE_SELECTING state\n"));
		dhcp->request_timeout = 0;
		/* remember offered lease */
		dhcp_handle_offer(netif);
	}

free_pbuf_and_return:

	if(dhcp != NULL) {
		dhcp->msg_in = NULL;
	}

	pbuf_free(p);
}

/**
 * Create a DHCP request, fill in common headers
 *
 * @param netif the netif under DHCP control
 * @param dhcp dhcp control struct
 * @param message_type message type of the request
 */
static err_t
dhcp_create_msg(struct netif* netif, struct dhcp* dhcp, u8_t message_type)
{
	u16_t i;
#ifndef DHCP_GLOBAL_XID
	/** default global transaction identifier starting value (easy to match
	 *  with a packet analyser). We simply increment for each new request.
	 *  Predefine DHCP_GLOBAL_XID to a better value or a function call to generate one
	 *  at runtime, any supporting function prototypes can be defined in DHCP_GLOBAL_XID_HEADER */
#if DHCP_CREATE_RAND_XID && defined(LWIP_RAND)
	static u32_t xid;
#else /* DHCP_CREATE_RAND_XID && defined(LWIP_RAND) */
	static u32_t xid = 0xABCD0000;
#endif /* DHCP_CREATE_RAND_XID && defined(LWIP_RAND) */
#else

	if(!xid_initialised) {
		xid = DHCP_GLOBAL_XID;
		xid_initialised = !xid_initialised;
	}

#endif
	LWIP_ERROR("dhcp_create_msg: netif != NULL", (netif != NULL), return ERR_ARG;);
	LWIP_ERROR("dhcp_create_msg: dhcp != NULL", (dhcp != NULL), return ERR_VAL;);
	LWIP_ASSERT("dhcp_create_msg: dhcp->p_out == NULL", dhcp->p_out == NULL);
	LWIP_ASSERT("dhcp_create_msg: dhcp->msg_out == NULL", dhcp->msg_out == NULL);
	dhcp->p_out = pbuf_alloc(PBUF_TRANSPORT, sizeof(struct dhcp_msg), PBUF_RAM);

	if(dhcp->p_out == NULL) {
		LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS,
		            ("dhcp_create_msg(): could not allocate pbuf\n"));
		return ERR_MEM;
	}

	LWIP_ASSERT("dhcp_create_msg: check that first pbuf can hold struct dhcp_msg",
	            (dhcp->p_out->len >= sizeof(struct dhcp_msg)));

	/* DHCP_REQUEST should reuse 'xid' from DHCPOFFER */
	if(message_type != DHCP_REQUEST) {
		/* reuse transaction identifier in retransmissions */
		if(dhcp->tries == 0) {
#if DHCP_CREATE_RAND_XID && defined(LWIP_RAND)
			xid = LWIP_RAND();
#else /* DHCP_CREATE_RAND_XID && defined(LWIP_RAND) */
			xid++;
#endif /* DHCP_CREATE_RAND_XID && defined(LWIP_RAND) */
		}

		dhcp->xid = xid;
	}

	LWIP_DEBUGF(DHCP_DEBUG | LWIP_DBG_TRACE,
	            ("transaction id xid(%"X32_F")\n", xid));

	dhcp->msg_out = (struct dhcp_msg*)dhcp->p_out->payload;

	dhcp->msg_out->op = DHCP_BOOTREQUEST;
	/* @todo: make link layer independent */
	dhcp->msg_out->htype = DHCP_HTYPE_ETH;
	dhcp->msg_out->hlen = netif->hwaddr_len;
	dhcp->msg_out->hops = 0;
	dhcp->msg_out->xid = lwip_htonl(dhcp->xid);
	dhcp->msg_out->secs = 0;
	/* we don't need the broadcast flag since we can receive unicast traffic
	   before being fully configured! */
	dhcp->msg_out->flags = 0;
	ip4_addr_set_zero(&dhcp->msg_out->ciaddr);

	/* set ciaddr to netif->ip_addr based on message_type and state */
	if((message_type == DHCP_INFORM) || (message_type == DHCP_DECLINE) || (message_type == DHCP_RELEASE) ||
	        ((message_type == DHCP_REQUEST) && /* DHCP_STATE_BOUND not used for sending! */
	         ((dhcp->state == DHCP_STATE_RENEWING) || dhcp->state == DHCP_STATE_REBINDING))) {
		ip4_addr_copy(dhcp->msg_out->ciaddr, *netif_ip4_addr(netif));
	}

	ip4_addr_set_zero(&dhcp->msg_out->yiaddr);
	ip4_addr_set_zero(&dhcp->msg_out->siaddr);
	ip4_addr_set_zero(&dhcp->msg_out->giaddr);

	for(i = 0; i < DHCP_CHADDR_LEN; i++) {
		/* copy netif hardware address, pad with zeroes */
		dhcp->msg_out->chaddr[i] = (i < netif->hwaddr_len && i < NETIF_MAX_HWADDR_LEN) ? netif->hwaddr[i] : 0/* pad byte*/;
	}

	for(i = 0; i < DHCP_SNAME_LEN; i++) {
		dhcp->msg_out->sname[i] = 0;
	}

	for(i = 0; i < DHCP_FILE_LEN; i++) {
		dhcp->msg_out->file[i] = 0;
	}

	dhcp->msg_out->cookie = PP_HTONL(DHCP_MAGIC_COOKIE);
	dhcp->options_out_len = 0;

	/* fill options field with an incrementing array (for debugging purposes) */
	for(i = 0; i < DHCP_OPTIONS_LEN; i++) {
		dhcp->msg_out->options[i] = (u8_t)i; /* for debugging only, no matter if truncated */
	}

	/* Add option MESSAGE_TYPE */
	dhcp_option(dhcp, DHCP_OPTION_MESSAGE_TYPE, DHCP_OPTION_MESSAGE_TYPE_LEN);
	dhcp_option_byte(dhcp, message_type);
	return ERR_OK;
}

/**
 * Free previously allocated memory used to send a DHCP request.
 *
 * @param dhcp the dhcp struct to free the request from
 */
static void
dhcp_delete_msg(struct dhcp* dhcp)
{
	LWIP_ERROR("dhcp_delete_msg: dhcp != NULL", (dhcp != NULL), return;);
	LWIP_ASSERT("dhcp_delete_msg: dhcp->p_out != NULL", dhcp->p_out != NULL);
	LWIP_ASSERT("dhcp_delete_msg: dhcp->msg_out != NULL", dhcp->msg_out != NULL);

	if(dhcp->p_out != NULL) {
		pbuf_free(dhcp->p_out);
	}

	dhcp->p_out = NULL;
	dhcp->msg_out = NULL;
}

/**
 * Add a DHCP message trailer
 *
 * Adds the END option to the DHCP message, and if
 * necessary, up to three padding bytes.
 *
 * @param dhcp DHCP state structure
 */
static void
dhcp_option_trailer(struct dhcp* dhcp)
{
	LWIP_ERROR("dhcp_option_trailer: dhcp != NULL", (dhcp != NULL), return;);
	LWIP_ASSERT("dhcp_option_trailer: dhcp->msg_out != NULL\n", dhcp->msg_out != NULL);
	LWIP_ASSERT("dhcp_option_trailer: dhcp->options_out_len < DHCP_OPTIONS_LEN\n", dhcp->options_out_len < DHCP_OPTIONS_LEN);
	dhcp->msg_out->options[dhcp->options_out_len++] = DHCP_OPTION_END;

	/* packet is too small, or not 4 byte aligned? */
	while(((dhcp->options_out_len < DHCP_MIN_OPTIONS_LEN) || (dhcp->options_out_len & 3)) &&
	        (dhcp->options_out_len < DHCP_OPTIONS_LEN)) {
		/* add a fill/padding byte */
		dhcp->msg_out->options[dhcp->options_out_len++] = 0;
	}
}

/** check if DHCP supplied netif->ip_addr
 *
 * @param netif the netif to check
 * @return 1 if DHCP supplied netif->ip_addr (states BOUND or RENEWING),
 *         0 otherwise
 */
u8_t
dhcp_supplied_address(const struct netif* netif)
{
	if((netif != NULL) && (netif_dhcp_data(netif) != NULL)) {
		struct dhcp* dhcp = netif_dhcp_data(netif);
		return (dhcp->state == DHCP_STATE_BOUND) || (dhcp->state == DHCP_STATE_RENEWING);
	}

	return 0;
}

#endif /* LWIP_IPV4 && LWIP_DHCP */
